Vapor compression still with liquid level cutoff



J. KIRGAN May 11, 1948.

VAPOR COMPRESSION STILL WITH LIQUID LEVEL CUT OFF Filed March 27, 1945 2Sheets-Sheet 1 m. ow mu QSSQ QW INVENTOR HISATTORNEY$ MSSS MSS@ mm wwwww um. mm t@ Patented May 11, 1948 UNITED' STATESv PATENT OFFICE VAPORCOMPRESSION STILALWITH LIQUID LEVEL CUTGFF .101m xii-gan, Elizabeth, N.J. Appiimlon March 27, 1945, se'riaiNo. 585,126 l .evaporating andrecovering liquid from a solution and improved apparatus for carryingout this method.

It is desirable in many operations to evaporate liquid from a solution.Such evaporation may be for the purpose of obtaining a solution ofhigher solute `concentration or to'recover liquid from the solution ina. purified state or for both such purposes. As an example in which theprocess is used to recover purified liquid, ships operating in saltwater require a supply of fresh waterfor use as boiler make-up. water orfor drinking purposes or both, and such fresh water is obtained byevaporating sea Water and condensing the vapor therefrom. Evaporatingand distilling apparatus for this and like purposesl should preferablyoperate continuously and ef.

ciently over long periods with a minimum of attention and maintenance.

Presently available equipment of the type describedl is unsatisfactoryin certain respects. The operation of such equipment is altered bychanges in the temperature of the sea water or other solution treated,by variations in Operating steam pressure and by other factorsnecessarily present in most installations and particularly in marineuse. The accumulation of salt in the. apparatus reduces the emciency ofits' operation and necessitates shutdowns for cleaning purposes with a.resultant drop in the amount of condensate produced. Under certainconditions of operation, known apparatus may flood or prime and as aconsequence a certain amount of salt water is carried over into thecondensate output. Constant skilled attention and adjustment is requiredto maintain the efliciency and output of known equipment of this type atsatisfactory levels, and lack of such attention and adjustmentfrequently results in flooding, priming or other failures or breakdownswhich are a serious hazard, particularly in shipboard installations wherthe evaporating equipment is the only sourc of fresh water available.

With the above and other condensations in mind, it is proposed inaccordance with the present invention to provide lan improved method ofand apparatus for evaporating solutions such as sea water and recoveringfresh water from the vapor so produced. 'Ihe invention contemplates anevaporation method and apparatus which operates continuously at highefllciency and productive capacity without any adjustment or attentionexcept that required to startthe operation and to shut it down. Inaccordance with the invention, the operation is maintained stable andeilicient despite changes in feed solution temperature, and otherAvariable factors. The apparatus of the invention preferablyincorporates improved protective devices so coordinated and interrelatedthat failures of operating steam supply, electric power or solutionsupply or withdrawal do not result in flooding, damage, or otherimpairment of the equipment.

In general, the invention involves the evaporation of vapor from asubstantially constant quantity of a solution such as sea Water under acontrolled absolute pressure, which may be below atmospheric pressure.The evaporating pressure is maintained by withdrawing vapor evolved fromthe solution and compressing it, the compressed vapor being employed tosupply heat to vaporize the solution. This heat interchange results inthe condensation of the withdrawn vapor. The vapor withdrawn from theevaporator is preferably compressed by the action of a heated fluid suchas steam, and the exhaust steam from this oper-ation is preferablymingled' with the compressed vapor and employed to heat the solutionvunder evaporation, the exhaust steam being condensed with the compressedvapor in this operation.

The solution is fed to and bled from a body of solution in theevaporator vessel so that the concentrated solution is withdrawnsubstantially continuously, and the .accumulation `of salt or othersolute, in Ythe evaporator is avoided. The amount of heat directlysupplied to the evaporating solutionby the compressed vapor and theexhaust steam where steam is used to compress the vapor is normally morethan is required to maintain vaporiz'ation at the rate vapor iswithdrawn by the compressor. This excess of supplied heat is deliveredto the solution being supplied to the evaporator. This is preferablyaccomplished by condensing a part of the vapor evolved in the evaporatorbefore it is compressed, by heat exchange with the relatively coldsolution being fed into the evaporator. The amount of vapor so condensedis controlled in accordance with the absolute pressure in theevaporator, preferably by varying the rate of feed of solution throughthe heat exchange means evaporatingl pressure is maintainedsubstantially constant at a value which may be so chosen as to provideeiicient and economical operation of the vapor compressing apparatus.scribed arrangement, variations in the temperature of the solution fedto the apparatus are compensated for by variations in the rate oi ow ofsolution therethrough, and a balance of heat input to and heat outputfrom the evaporating and condensing equipmentr is maintained. Thus whenthe temperature of the feed solution rises so as to more closelyapproach the evaporating temperature, the rate of feed of the solutionis increased, whereas a drop in feed solution temperature results in alowered rate of solution feed.

A preferred form of the invention includes a condenser or heatexchanger, which may also be termed a heat balancer, which condenses apart of .the uncompressed vapor evolved in the evaporator by heatexchange with the relatively cold solution fed to the evaporator. Thecondensate resulting from this operation together with that resultingfrom condensation of the compressed vapor and the exhaust steam' fromthe vapor compressing apparatus constitutes the condensate output of theequipment.

In a. preferred form of the invention, a steam With the dejet evacuatoror thermal compressor is employed to withdraw vapor from the evaporatorand compress it. Mechanical compressors might be used for this purpose,but the steam jet type is preferable because it is eilicient andreliable and requires little or no maintenance over extended periodsl ofoperation. The amount of vapor propelled by a steam jet evacuator inrelation to the amount of motive steam consumed varies with the suctionpressure, and since the absolute pressure in the evaporator of my systemis maintained substantially constant in the manner described, the steamjet device may be employed to withdraw and compress the vapor in ahighly eflicient and economical manner.

In one form of the invention, the solution iS maintained under pressurewhile heat is delivered thereto from the compressed vapor and exhauststeam, and the heated solution is flashed in the evaporator, the heatbalance being maintained in the manner described above. This arrangementprevents ebullition of the solution in contact with heating surfaces,and so minimizes or eliminates the accumulation of salt deposits in theapparatus.

In describing the invention in detail, reference will be made to theaccompanying drawings in which typical apparatus embodying the inventionand capable of performing the improved method has been diagrammaticallyillustrated. In the drawings:

Fig. 1 is a diagrammatic and simplified representation of a solutionevaporating system embodying the invention and capable of carrying outthe method of the invention;

Fig. 2 is a diagrammatic and simpliied representation of a modified formof solution evaporating system embodying the invention; and

Fig. 3 is a diagrammatic elevation of a vapor compressor and drivingmeans therefor which can be employed in the embodiments of Figs. 1 or 2in place of the steam jet evacuators or thermal compressorsthereillustrated.

The invention will be described in connection with systems for use inevaporating and condensing brine such as seawater to produce fresh waterfor use on shipboard. The invention is obviously not limited to thisapplication but is useful in any operation involving evaporation of'water or other liquid from a solution.

Referring to the system illustrated in Fig. 1, it includes anevaporator4 comprising a closed vessel of any suitable shape having avapor outlet duct 5 connected through its top wall and a solution outletpipe 6 connected to its bottom wall. 4.A brine supply pipe 'I isconnected to the evaporator through an intermediate point.

The solution to be treated, which in the embodiment shown comprises saltsea water or brine, enters the system under pressure in the pipe 8. Thebrine may be supplied under pressure by any suitable means such as abrine pump. commonly remployed in marine installations. From the pipe 8,the brine flows through the tubes I3 of a condensate cooler 9,thenthrough tem constant, and through the pipe II to a heat I exchangeunit l2 which is herein termed a heat balancer. The condensate cooler 9,which is not essential to the invention in its broader aspects, may beof any conventional construction and as shown has a shell I4 surroundingthe tubes I3 to carry 1 condensate in heat exchanging relation with theincoming cold brine in the tubes.

The heat balancer. I2 is also of conventional heat exchangerconstruction and as shown comprises a shell I4 through which vapor fromthe evaporator 4 passes between the duct 5 and the duct I5 over thetubes I6, suitable bailles I1 being provided to direct the vapor in acircuitous path over the tubes. Brine from the pipe II is conductedthrough the tubes I6 and then through a pipe I8, a control valve I9 andinto the evaporator 4 through the pipe 1.

A separator, represented as a series of bailles 20, is provided in theupper end of the evaporator 4 to remove any entrained liquid from theorate the same. Various means may be employed to compress the vapor. Inthe embodiment disclosed in Fig. l, a steam jet evacuator or thermalcompressor 2| of known construction is employed for this purpose. Asshown, the intake of the evacuator is connected to the vapor duct I5,and the motive steam from a boiler or other suitable source is suppliedto the jet of the evacuator through a pipe 22 under control of a valve23. The .compressed vapor and exhaust steam from the evacuator 2| isconducted by a duct 24 to the shell of a heat exchanger 25 where itiiows over the tubes 26 between the bailles 21 and is condensed, thecondensate being drawn ol! in a well 28 and a pipe 29. The pipe 29 isconnected to the shell I4 of the condensate cooler 9 where thecondensate ilows in heat exchanging relation with the cold incoming seawater and is drawn oi through the pipe 3U by a condensate removal pump3l and delivered to a condensate storage tank, not shown. In thedisclosed embodiment, the condensation of vapor and steam in the heatexchanger 25 takes place at atmospheric pressure, and accordingly anatmospheric vent 66 is connected to the shell of the evaporator 25.

In place of the steam jet evacuator or thermalcompressor 2l shown inFig. 1, a mechanical compressor may be employed to withdraw and compressvapor from the evaporator 4 and deliver it to the heat exchanger 25.Such an arrangement has been illustrated in Fig.3, where a compressor 99is illustrated. The intake port 9i of this compreor may be connected tothe vapor duct Il. and the outlet port 92 thereof may be connected tothe pipe 24 leading to the heat exchanger 2l. As shown in Fig. 3, thecompressor 99 is driven by a steam turbine 93.V and the errlmust steamfrom this turbine flows through a pipe 94 into the pipe 24. Motive-steamfor the turbine is supplied thereto through a pipe 95 which may be acontinuation of the supplyI pipe 22 of Fig. 1.

The body of brine or other solution in the evaporator 4 is preferablykept relatively constant by suitable means such as a iloat control. Asshown, a brine circulating pump 33 withdraws brine from the evaporator 4through the pipe 8 and delivers it through` a pipe 34 to the tubes 28 ofthe heat exchanger and hence through a pipe 35 to a spray pipe 35 withinthe evaporator `4. 'I'he spray pipe 35 is disposed above the liquidlevel in the evaporator and is provided with restricted openings forpermitting the solution to spray or flash within the evaporator ashereinafter explained.v

A iloat 31 acting through the levers 38 and 39 and the link controls afloat valve 4I' in a branch pipe 42 leading from the pump outlet pipe34. I'he arrangement is such that when the liq.

uid in the evaporator 4 rises above a predetermined level, the float 31opens the valve 4I and permits some of the brine to ow outof the systemthrough a waste pipe 43.

Distillate from the heat balancer I2 ilows through a pipe 44 which maybe connected to the well 24 of the heat exchanger 25 through a U trap,as shown. The trap is employed to prevent flowing back of vapor orcondensate from the heat exchanger 25 to the heat balancer I2, the heatbalancer normally being at an absolute pressure considera-bly below thatin the heat exchanger 25. Fior the purpose of quickly filling theevaporator 4 and the connected liquid circuit through the heat exchanger25 with sea water, a pipe 45, provided with a manually operable valve48, is connected between the sea water supply pipe 8 and the brinecirculating pipe 34.

In accordance with the invention, it is preferred to govern theoperation of the system by varying the rate at which the solution issupplied to the evaporator 4 through the heat balancer I2, the rate ofevaporation being maintained su'bstantially constant. To this end and toobtain certain protective features, the control mechanism illustrated inFig. 1 isprovided.

The now on! sea water into the evaporator 4 through the circuitincluding the tubes I8 of the heat balancer I2 is governed by athrottling control valve I9 which is preferably automatically controlledin accordance with the absolute pressure at which evaporation is takingplace in the evaporator 4, or in accordance with the temperature of suchevaporation, which varies with such absolute pressure. As shown, thevalve I9 is of the diaphragm operated type, being closed by a spring 41and opened when pressure of a uid in its diaphragm chamber 48 exceedsthe pressure oi' the spring.

In the illustrated embodiment, the sea water, which is maintainedundercontrolled pressure, is used as the valve actuating control fluid.A control vfluid supply pipe 49, connnected to the sea water supply pipeIl, is connected through 6 a needle valve 50, a relief valve Il, thepipes 42 and 53 and a needle valve I4 and the pipes '55Vv and 58 to thediaphragm chamber 44 oi' the valve I9. 'I'he valve element 51 of therelief valve 5I is normally in the lower position shown to complete thedescribed circuit.

'I'he liquid pressure in the diaphragm chamber 48 is controlled inaccordance with the absolute pressure of evaporation by a throttlingvalve 58 in a waste pipe 59 connected to the pipes 55 and 58. Theopening of the valve 58 is preferably automatically governed inaccordance with the absolute pressure of evaporation. Pressurecontrolled valves of this type are well known and the construction ofthe valve operating mechanism'will not be described in detail. ,Asshown, a tube 50 connects the operating mechanism of the valve `58 to asuitable point in the evaporator or the ducts maintained at evaporatorpressure. Inthe illustrated embodiment, the tube 80 runs to the duct I5ythrough which vapor is withdrawn from the evaporator by the evacuator2|. The arrangement is such that when the absolute pressure in theevaporator 4 increases above a predetermined value, the valve 58 ismoved toward a closed position, causing an increase in the pressure ofthe water in the pipe 58 and the diaphragm chamber of the valve I9,thereby increasing the opening of the valve I9 and hence increasing therate of flow of sea water through the heatbalancer I2 and into theevaporator 4. If the absolute pressure in the evaporator 4 falls below apredetermined value, the valve 58 moves toward its fully openedposition, permitting the ilow of an increased quantity of water throughthe waste pipe 59 and hence reducing the pressure in the diaphragmchamber of the valve I9, whereupon the spring 41 throttles the valve I9and the rate of flow of sea water into theevaporator 4 is reduced.

The control valve 58 may be operated directly by the absolute pressureof evaporation or lndirectly in accordance with such pressure bytemperature responsive means of known construction which is responsiveto the temperature of the liquid or vapor in the evaporator 4. The.

temperature in the evaporator changes in direct proportion to thechanges in absolute pressure therein, and the described control may beobtained by substituting a thermal bulb for the pressure connection sothat the valve 58 vwill be closed by an increase in temperature andopened by a drop in temperature from a predetermined value correspondingto the desired absolute pressure of evaporation.

The motive steam supply valve 23 is of the same type as the abovedescribed sea water control -valve I8, and is closed by a spring 8| andopened by fluid pressure in a diaphragm chamber ,82 acting against thepressure of the spring.

As shown, the diaphragm chamber 82 of the valve 23 is supplied with seawater under pressure through the pipe 83 connectedto the pipe 52. A

waste pipe 84 having a needle valve $5 therein is connected to the pipes52 and 53.' With this arrangement, the steam supply valve 23 ismaintained open so long as the sea water in the pipes 52 and 83 ismaintained under pressure. The needle valve 58 is set at a considerablylarger opening than the needle valve 95, so that as long as the element51 of the relief valve 5I is in the lower position as shown, suflicientsea water is fed to the pipes 52 and 83 to maintain a pressure thatholds the steam valve 23 open despite the leakage of sea waterthroughthe needle valve 65 in the waste pipe 84. When the element 51 of therelief valve rises to its upper position, the supply of sea water t6 thepipe 52 is eut oil' and thepipe 49 is vented to waste, the needle valve50 restricting the flow to waste under this condition. Thereupon, thesea water pressure on the diaphragm chamber B2 of the steam valve 23drops due to leakage through the needle valve 55, and the steam valve 23closes. This drop in sea water pressure also results in closing of thevalve I9.

The relief valve 5| is operated by a solenoid 61 which lowers the valveelement 51 to the position shown when energized and raises this elementwhen de-energized. The solenoid B1 is maintained energized by a circuitthat is opened upon failure or improper operation of certain elements ofthe system, as will now be explained.

The brine circulating pump 33 is driven by a motor 58 and Jthecondensate removal pump 3| is driven by a motor 59. The motors 58 and 89may be polyphas'e inducting motors as indicated, although other typemotors may be used. The motors are energized from a source representedby the terminals 10 through a. manually operable main switch 1|, apressure operated switch 12 and two branch circuits respectivelyincluding overload cutout protective devices of known constructionherein conventionally represented as fuses 13 and 14'. The pressureoperated switch 12 is of known construction and is arranged to close itscontacts when a predetermined pressure is applied to its operatingdiaphragm chamber 15, and to open its contacts when lthis pressure fallsbelow a predetermined value.- The diaphragm chamber 15 is connected by apipe 16 to the pipe I| which normally carries sea water un` dercontrolled pressure.

The energizing circuit for the solenoid 61 of the relief valve 5I is aseries circuit running from one phase lead of the brine pump motor 88 tothe solenoid 51 through the wire 11, then through the wire 18 to a highlevel brine iloat switch 19 in the evaporator 4, then through the wire80 to a high level condensate float switch 8| in the condensate well 28and then through a wire 82 to a phase lead of the condensate removalpump motor 59 which is in a diierent phase of the supply circuit thanthe lead to which the wire I 11 is connected. The switches 19 and 8| areof known construction and normally maintain the described circuitclosed, but open if the liquid level in the evaporator 4 or in thecondensate well 28 rises above a predetermined level. A lamp 8`4 orother signal may -be connected between the wires 11 and 18 in parallelwith the solenoid 61 to indicate operation of the system. This lamp orsignal may be located at a pointconvenient to the operator and indicatesproper operation of the system when energized.

With the arrangement described above, the solenoid 61 is maintainedenergized so long as the pressure of the sea water in the pipe Il is ator above a predetermined value, the motors 68 and 69 are operating andthe liquid levels in the evaporator 4 and the condensate well 28 do notexceed the desired maximum values. If the overv load cutout device 13 or 14 'of either of the m-otors 58 or 69 opens due to an obstruction inthe corresponding pump or for any other cause, the solenoid 61 isde-energized. Likewise an increase in the evaporator brine level above apredetermined point opens the solenoid energizing circuit at the switch19 and an'increasein the con- De-energization of the solenoid 81 raisesthe element 51 of the relief valve 5|, cutting off the supply of seawater pressure from the pipe 52 whereupon this pressure is ventedthroughv the pipe 64 to waste. thus closing the steam supply valve 23and the sea water control valve I9 in the manner explained above.

The operation of the embodiment o! the invention illustrated in Fig. 1will now be described. To start the operation, salt sea water or othersolution is admitted to the system by opening the valve 83 in the supplypipe 8. If the evaporator 4 is empty, it 'can be quickly iilled to thedesired level by opening the valve ,46 in the pipe 45 for an interval.When sulcient sea water has been admitted to the evaporator to fill itto 'approximately the level indicated in the drawing, the main switch 1|is closed. The pressure of the sea water in the pipe closes the pressureswitch 12 and the pump motors 68 and 89 start and operate the pumps 33and 3| respectively. At the same time, the solenoid 81 is energized andthe element 51 of the relief valve 5| is lowered. Sea water pressurethen builds up in the diaphragm chamber 62 of the steam supply valve 23and opens this valve which admits motive steam to the steam jetevacuator or thermal compressor 2|.

The evacuator 2| quickly reduces the pressure in the evaporator 4 to orbelow the desired operating value, which in the disclosed embodiment isa sub-atmospheric value. `At the start of the operation, substantiallyno evaporation takes place, and the absolute pressure in the evaporatoris rapidly reduced. When the evaporator pressure is above the desiredworking value, the control valve 58 is closed and the sea water supplyvalve I9 is accordingly open, permitting sea water to flow into theevaporator 4. The excess sea water ows to waste through the pipes 42 and43 under control oi the float valve 4|. As soon as the evaporatorpressure is reduced as described to I livers heat to the brine throughthe heat ex` changer 25, and since this brine is continuously circulatedthrough the tubes 28 of the heat exchanger, the body of brine in theevaporator 4 and in the heat exchanger 25 is heated up. The exhauststeam is condensed by this heat exchange and the condensate ilows intothe well 28. When the temperature of the brine in the evaporator 4 risesto a value near the working value, evaporaticn of water from the brinetakes place in the evaporator. The capacity of the pump .33 is sorelated to the size of the openings in the spray pipe 3B that the brineis kept under sufiicient pressure in the heat exchanger tubes 26 toprevent its ebullition therein at the working temperature. When thebrine temperature is at or near the working temperature, the reductionof the pressure thereon upon passing through the spray pipe openings andinto the evaporator causes a part of the water in the brine to ilash orvaporize, the more concentrated brine falling into tlie body of brine inthe evaporator,

The described heating up of the brine continues until the brinetemperature and the absoevaporator at a rate somewhat greater than therate at which vapor is withdrawn therefrom and compressed by theevacuator 2|. Thus the absolute pressure in the evaporator 4 tends torise. Any increase in absolute pressure in the evaporator above apredetermined value moves the control valve 58 toward its closedposition, increasing the sea water pressure on the diaphragm chamber 48vof the sea water control valve I9 and so opening this valve. Relativelycold sea water then iiows from the pipe through the tubes I6 of the heatbalancer I2, through the pipes I8 and 1 and into the evaporator 4. Allof the vapor evolved in ,the evaporator 4 is drawn through the shell ofthe heat balancer I2 by the evacuator 2|, and the flow of sea waterthrough the heat balancer tubes I6 causes condensation of' some of theevolved vapor within the heat balancer shell, the resulting distillateflowing through the trapped pipe 44 to the condensate well 28. Thiscondensation of a part of the uncompressed vapor reduces the absolutepressure in the evaporator, and when the desired working pressure isrestored, the control valve 58 moves toward its open position and thesea water control valve I 9 moves toward its closed position until theopening of the valve I9 is such that the system is balanced, that is,evaporation takes place at a substantially constant temperature andpressure with a continuous ow of sea water into the evaporator anddischarge of sea water from the system through the pipe 43. Thecontinuous feed of sea water and discharge of concentrated brineprevents the accumulation of salt or other solute in the evaporator orin other parts of the system.

The described arrangement in which all of the vapor evolved in theevaporator 4 is drawn through the heat balancer I2 by the evacuator 2|prevents the accumulation of air in the heat balancer. Air and othernon-condensible gas is introduced into the evaporator as entrained air,as dissolved air in the water, and through air leaks, particularly whereas in the present system the evaporator operates at sub-atmosphericpressure. The accumulation of air in a condenser or heat exchangerlowers the heat transmission emciency of its heat exchanging surfaces.In the present system, the vapor evolved in the evaporator entrains anyair that may be present and carries it through the heat balancer I2 andthe evacuator 2| and finally into the heat exchanger 25 from which theair escapes to atmosphere through the vent 66. 'I'he accumulation of airin the system is thus prevented without the necessity for using an airwithdrawal pump or purger.

The distillate from the heat balancer I2 and condensate from the heatexchanger 25 collect in the well 28 and are drawn oi as the totalcondensate produced through the pipe 29 and the tubes 3 of thecondensate cooler 9 by the pump 3| which delivers the condensate tostorage. Some of the sensible heat in the condensate is recovered anddelivered to the incoming sea water by exchange in the condensate cooler9. The condensate cooler is not essential to the invention and may beomitted. If desired, the distillate from the heat balancer I2 may bedrawn ofi separately and used for drinking purposes, since thisdistillate is not condensed from boiler steam and is free from any oilor other impurities that may be present in steam from aboiler.

It should be noted that in the above described operation of my system,the steam supply and the rate of evaporation are kept substantiallyconstant and the only variable control is the corrective variation ofthe rate of flow of sea water to the evaporator and out of the system.This corrective control is governed by departures of the absolutepressure in the evaporator, or, what is the same thing, in the vaporintake of the steam jet evacuator, from the desired working value.

Heat is supplied to the system by the motive steam and in the form ofthe sensible heat in the sea water. The heat supplied by the motivesteam acts in part to compress the vapor withdrawn from the evaporator 4by the evacuator 2|, and the heat of the compressed vapor and of theexhaust steam is delivered to the brine in the evaporator through theheat exchanger 25. The heat so delivered includes the latent heat ofVaporization of the vapor and steam and some vapor heat oi thecompressed Vapor and sensible heat of condensate, the remainderappearing as sensible heat in condensate that is drawn off through thepipe 29. The heat transferred to the brine by condensation of thecompressed vapor and exhaust steam is in excess of that required toevaporate vapor at the rate that vapor is withdrawn from the evaporator4 by the evacuator 2|, and the excess vapor is condensed in the heatbalancer I2. In a typical installation, about '75% of the vapor evolvedis withdrawn and compressed by the evacuator 2|, and the remaining 25 iscondensed in the heat balancer I2.

The heat supplied to the system acts to increase the sensible heat ofthe sea water to the boiling point at the controlled evaporationpressure and to supply the latent heat of vaporization to maintainevaporation, and the excess heat over that so employed passes off in theconcentrated brine that is pumped overboard and in the condensate fromthe heat balancer I2 and the heat exchanger 25. Some additional heat islost by radiation from the apparatus, but this loss may be kept very lowby proper insulation.

If the temperature of the sea water or other solution treated rises, theabsolute pressure of evaporation tends to increase with a resultantincrease in the opening of the sea water control valve I9, and the rateof ow of sea Water into the evaporator 4 through the tubes of the heatbalancer I2 increases. This restores the desired rate of condensation inthe heat balancer and maintains the absolute pressure of the evaporatorat the desired value with an increase rate of ow of sea Water to theevaporator and an increased rate of discharge of brine from the system.The amount of.heat loss from the system does not changeappreciably withthe increased rate of brine discharge because the diierence intemperature between the incoming sea water and the discharged brinedrops. This necessarily results since evaporation takes place at asubstantially constant temperature, and any increase in the temperatureof the incoming sea water necessarily reduces this temperaturedifference. Since less sensible heat is added to bring the sea Water tothe boiling point at the xed evaporating pressure, a slightly increasedamount of heat is removed inthe discharged brine to maintain the heatbalance o1' the system.

A drop in temperature of the incoming sea water has the reverse eiiect.It results in temporarily increasing the rate of condensation of vaporin the heat balancer I2 which tends to reduce the absolute pressure inthe evaporator 4. This results in a reduction in the opening of the seawater control valve I9 and a consequence reduction in the rate of supplyof sea water to the evaporator. This in turn reduces the rate of 1lcondensation in the heat balancer I2 to the desired value and restoresthe desired evaporation pressure. The rate of brine discharge falls withthe reduced sea water input and the systernjcon-` tinues to operate inbalance with constant evapmatically in the manner described over therange Y of input sea water or other solution temperatures that are metwith in practice. The normal operation of the system is automatic andself controlled and changes in the input solution temperature areautomatically compensated for by changes in the rate of solutionthroughput. Since the absolute pressure at which evaporation takes placeand thus the suction pressure on the evacuator 2| is maintainedsubstantially constant, the evacuator may be operated in a highlyeiiicient and economical manner.

When a mechanicalv compressor such as the device 9| of Fig. 3 issubstituted for the steam jet evacuator 2|, the operation of the systemis unchanged. The exhaust steam from the compressor driving turbine 93is mixed with. the compressed vapor in the pipe 24' and deliveredtherewith to the heat exchanger 25. The steam supplied to operate theturbine 93 thrcugh the pipe 95 is controlled by the steam control valve23 in the manner explained above in connection with the evacuator 2|.

The above described protective devices prevent flooding of the system oriniury thereto in case of failure of electric power or` of the-pumpingequipment, clogging of pipes or'failure of the sea water supply. If theelectric power fails. the pump motors 68 and 69 stop and the solenoid 61is deenergized, bleeding off the control pressure from the pipes 52, 53,63. 55 and 56 and so closing the steam supply valve 23 and the sea Waterinlet valve I9. overloading of either pump motor has the same effectsince when either of the motor overload protective devices 13 or 14opens, the solenoid 61 is de-energized. Similarly,

a drop in supply sea water pressure due to any failure in the pumpingequipment or the supply ducts opens the pressure switch 12 andde-energizes the solenoid 61. In each of the above cases. the hot brineis retained in the evaporator 4 and undue heat' loss from the system bydischarge of the brine is avoided. Failure of the condensate or brinepumps 3l or 33 to remove the evaporator.

the condensate or brine which might result from clogging of the pipesleading to or from these pumps increases the level of condensate in thewell 28 or of brine in the evaporator 4. 'I'his opens the float switches8| or 19, and in either case the energizing circuit for the solenoid 61is opened with the result that the steam and sea water supply valves 23and I9 are closed. In such a case, the pumps 3| and -33 continue t'ooperate unless they are stopped by an overload or a failure of supplysea water pressure. Any failure results in de-energization of thesolenoid 61 and the accompanying de-energization of the signal device 84informs the operator or supervisor of the shutdown.

The system disclosed in Fig. 2 differs from that of Fig. 1 in that heatfrom the compressed vapor and exhaust steam is transferred to the brinewithin the evaporator directly through a tube bundleand causesebullition and vaporization of the brine directly from the body of brinein the evaporator rather than'by spray flashing. Many of the devicesemployed in thetwo systems are identical, and the description of suchparts will not be repeated. Parts of the system of Fig. 2

which correspond to previously described parts of the system of Fig. 1will be deslgnatedvby like reference characters with distinctiveexponents.

The evaporator 4' is provided with a tube bundle |00 disposed therein atsuch a position that the greater part of the tube bundle is submergedwhen the brine level in the evaporator is at or near the desired pointillustrated. As shown, the tube bundle |00 may extend `laterally intothe evaporator 4' adjacent the lower end of The tube sheet |0| of thebundle |00 is suitably secured to the shell of the evaporator 4' aboutan opening therein through which the tube bundle |00 extends, and a heador manifold |02 secured over the tube sheet |0| directs compressed vaporand exhaust steam from the evacuator 2|' and duct 24' through the tubesof .the bundle. The head |02 and the tubes connected thereto are ventedto atmosphere by a pipe |03. Condensate from the tube bundle |00collects in the well 28', and the distillate discharge pipe I4' from theshell I4' of the heat balancer I2' is also connected to the well 28', atrap being provided in the pipe 44 to prevent reverse flow of condensatedue to the pressure dierence between the tube bundle |00 and the heatbalancer I2'.

Brine is removed from the evaporator 4' by a pump 33 connected by a pipe6 with the lower end of the evaporator. The discharged brine iiowsoverboard or to waste through a pipe 43' under control of a valve 4|controlled by a iloat 31' to maintain a substantially constant liquidlevel in the evaporator 4'.

Condensate and distillate from the well 28 is drawn off by thecondensate pump 3|' through the pipe 29', the shell I4' of thecondensate cooler 9' and the pipe 30', and the condensate is deliveredto the storage tank, not shown. The remainder of the apparatuscomprising the system of Fig. 2 is in all respects the same as that ofFig. 1. It should be understood that in the lsystem of Fig. 2, a steamdriven mechanical compressor such as the compressor 9| of Fig. 3 may besubstituted for the steam jet evacuator 2|' in the same manner as hasbeen explained above in connection with the system of Fig. 1.

The operation of the system of Fig. 2 is substantially the same as thatdescribed above in connection with the system of Fig. l. The evaporator4 is filled with solution to substantially the indicated level, thevalve 46' in the pipe 45' being opened for this purpose. With the valve83' in the pipe 8' open, the switch 1I' is closed, and sea waterpressure in the pipe closes the pressure switch 12', starting the pumpmotors 68' and 69' and energizing the solenoid 61' to lower the element51' and so close the waste pipe of the relief valve 5|. The steam valve23 then opens, starting the evacuator 2|' and lowering the pressure inthe evaporator 4. Before the absolute pressure in the evaporator islowered to the desired working value, the sea water supply valve I9' isopen, but the liquid level in the evaporator is maintained constant byremoval of liquid therefrom by the pump 33' under control of the oatvalve 4|'. evacuator 2|' ows through the pipe 24' and the tubes of thebundle |00, heating up the brine The exhaust steam from the balancerI'Z, and the duct l5'.

ration takes place and the evolved vapor 'is withfdrawn through theseparator illustrated as the bailles 20', the duct 5', the shell I l' 0fthe heat The withdrawn vapor is compressed up to atmospheric pressure inthe evacuator 2|' .and delivered through the pipe 24. The compressedvapor and exhaust steam are condensed in the tube bundle and thecondensate collects in the well 20' and is drawn off by the pump 3|'.Distillate from the heat balancer l2' flows into the well 28' throughthe pipe 44" and is drawn off with the condensate. The distillate may bedrawn o separately for use as drinking water if desired.

The system of Fig. 2 is so controlled as to maintain a substantiallyconstant absolute pressure in the evaporator 4', and this pressure is sochosen as to insure economical and eiiicient operation of the evacuator2 I The amount of heat delivered to the brine in the evaporator 4 bycondensation from the compressed vapor and exhaust steam in the tubebundle |00 is in excess of that required to evolve vapor at the rate7vapor is withdrawn by the evacuator 2|', and the excess is condensed inthe heat balancer I2'. At the operating evaporation pressure, the seawater supply valve i9' is partly open so that there is a constant inputand withdrawal of brine through the evaporator. Increases in absolutepressure in the evaporator 4' above the desired working value arecompensated for by increases in the rate of flow of sea water throughthe tubes I6 of the heat balancer l2', the opening of the sea watercontrol valve i9' being increased by the action of the control valve 58'which responds to the changes in absolute pressure in the duct I or tochanges in temperature in the evaporator which correspond to suchabsolute pressure changes. A rise in incoming sea water temperaturetends to increase the pressure in the evaporator l' and results in anincrease in the rate of sea. water input. Conversely, a drop in incomingsea water temperature results in a decrease in sea water input, and thepressure and rate of evaporation in the evaporator I' are maintainedsubstantially constant. Any air that may be present in the evaporator lis removed therefrom and from the heat balancer |'2 by the vapor whichpasses in series through the evaporator and heat balancer, and this airescapes to atmosphere through the vent |03.

The system of Fig. 2 is protected against failure of electric power,overloading of the pump motors 68' or 69', clogging of the condensate-orbrine removal pumps or ducts and failure of sea water supply pressure inthe same manner as has been described in connection with the system ofFig. 1. Failure of supply sea water pressure or electric power, overloadde-energization of either of the pump motors 08' or 00' or rise in theliquid level in the evaporator I' or the condensate well 28 de-energizesthe solenoid 01' and lifts the element B1' of the relief valve 5I',venting the control sea water and closing the steam supply valve 23' andthe sea water supply valve IS'. De-energization of the solenoid 61 isaccompanied by de-energization of the signal device 84' whereby theoperator is informed of the failure or shutdown.

From the foregoing, it will be apparent that the evaporation system andmethod of my invention present many advantageous features.

Once started up, the system operates automatically and continuously overlong periods without attention. Evaporation and condensation ,proceed ata substantially constant rate despite changes in the temperature of theincoming sea water, and such changes do not materially aiect theoperating emciency of the system. The throughput of sea water insuresthe removal of salt or other solute from the evaporator, and shutdownsfor removing solute accumulations are avoided. The system is protectedagainst failures of power or solution supply, clogging or overloadingsuch as may occur in practice. The design of the system is such that itmay be economically constructed and arranged in a very compact form.Since the system is at all times maintained in a balanced condition withrespect to heat input and dissipation, the suction pressure on theevacuator or other compressor is maintained constant, and this pressurecan be so chosen as to insure eiiicient operation of the vaporcompressing mechanism.

Although my invention has been described in connection with anevaporation system designed primarily for treating sea water to obtainfresh water in marine installations, it should be understood that theinvention is not limited to such applications. It can be used toconcentrate solutions or to remove liquids from solutions whenever suchoperations are desired in the industrial and chemical iield generally.yThe temperature and absolute pressure of evaporation and disposal of theconcentrated solution and the condensate and distillate can be varied tosuit the particular application and the results to be accomplished.

I claim:

1. Evaporation apparatus *comprising an evaporator for enclosing -asolution to be evaporated, a compressor connected to withdrawvapor fromsaid evaporator and compress the same, means for conducting said vaporfrom said compressor into heat exchanging relation with the solution insaid evaporator, means for supplying solution to said evaporator, meansfor withdrawing solution from said evaporator, means responsive to theliquid level of solution in said evaporator for controlling theoperation of said withdrawal means whereby the solution in saidevaporator is maintained at a predetermined level, means for conductingthe supplied solution in heat exchanging relation Wlth the vapor beingwithdrawn from the evaporator whereby a part of said vapor is condensed,and means responsive to an increase in the liquid level of solution insaid evaporator above said predetermined level i for stopping saidsolution supply and withdrawal means and said compressor.

2. Evaporation apparatus comprising an evaporator for enclosing asolution to be evaporated, a compressor connected to withdraw vapor fromsaid evaporator and compress the same, means for conducting said vaporfrom said compressor into heat exchanging relation with the solution insaid evaporator, means for supplying solution to said evaporator, meansfor withdrawing solution from said evaporator, means responsive to theliquid level of solution in said evaporator for controlling vtheoperation of said withdrawal means whereby the solution in saidevaporator is maintained at a predetermined level, means for conductingthe supplied solution in heat exchanging relation with the vapor beingwithdrawn from the evaporator whereby a part of said "vapor condensed,means responsive to the absolute pressure of the vapor in saidevaporator for variably controlling the rate at which solution issupplied to saidevaporator, and means responsive to an increase in theliquid level of solution in said evaporator above said predeterminedlevel for stopping said solution supply and withdrawal means and saidcompressor.

3. Evaporation apparatus comprising an evaporator for enclosing asolution Ito be evaporated, means for supplying a solution to saidevaporator, a compressor connected to withdraw vapor from saidevaporator, heat exchange means for conducting compressed vapor fromsaid compressor into heat exchanging relation with the solution in saidevaporator, a pump for withdrawing solution from said evaporator, meansresponsive toi the liquid level in said evaporator for controlling therate at which solution is withdrawn by said pump whereby the amount ofsolution in said evaporator is maintained substantially constant at a.predetermined value, and means responsive to a rise in the level 'ofsolution in said evaporator above said predetermined value for stoppingsaid pump, discontinuing the supply'of solution to said evaporator andstopping said compressor.

' 4. Evaporation apparatus comprising an evaporator for enclosing asolution to be evaporated, means for supplying a solution to saidevaporator, a compressor connected to withdraw vapor from saidevaporator, heat exchange means for conducting compressed vapor fromsaid compressor into heat exchanging relation with the solution in saidevaporator, whereby heat is supplied to evaporate solution in saidevaporator and said compressed vapor is condensed, a pump forwithdrawing condensate from said heat exchange means, a second pump forwithdrawing solution from said evaporator, means responsive to theliquid level in said evaporator for controlling the rate at whichsolution is withdrawn by said second pump wherebythe level of solutionin said evaporator is maintained substantiallyconstant at apredetermined value, means for driving each of said pumps and meansresponsive to stoppage oi' either of said pump driving means fordiscontinuing the supply of solution to said evaporator and stoppingsaid compressor.

5. Evaporation apparatus comprising an evaporator for enclosing asolution to be evaporated, means for supplying a solution to saidevaporator, a compressor connected to withdraw vapor from saidevaporator, heat exchange means for conducting compressed vapor fromsaid compressor into heat exchanging relation with the solution in saidevaporator, whereby heat is supplied to evaporate solution in saidevaporator and said compressed vapor is condensed, a pump forwithdrawing condensate from said heat exchange means, a second pump forwithdrawing solution from said evaporator, means responsive to theliquid level in said evaporator for controlling the rate at whichsolution is withdrawn by said second pump whereby the level of solutionin said evaporator is maintained substantially constant at apredetermined value, means for driving each of said pumps and meansresponsive to a stoppage of either of said pump driving means and to arisei'n the level of solution in said evaporator above saidpredetermined value for discontinuing the supply of solution to saidevaporator and stopping said compressor.

6. Evaporation apparatus comprising an evaporator for enclosingasolution to'be evaporated. a source of solution under pressure, meansfor supplying solution from said source to said evap orator, acompres-sor for withdrawing vapor from said evaporator, heat exchangemeans for conducting vapor from said compressor into heat exchangingrelation with the solution in said evaporator whereby heat is suppliedto evaporate solution in said evaporator and said. compressed vapor` iscondensed, a pump for withdrawing condensate from said heat exchanger, asecond pump for withdrawing solution from said evaporator, means foroperating said pumps, and means responsive to a ,decrease in thepressure. of the solution from said source below a predetermined valuefor stopping said pump operating means, discontinuing the supply ofsolution to said evaporator and stopping said compressor.

7. Evaporation apparatus comprising an evaporator for enclosing asolution to be evaporated, means for supplying solution' to saidevaporator, a compressor for withdrawing vapor from said evaporator,yheat exchange means for conduct- 'ing compressed vapor from saidcompressor ,into

heat exchanging relation with the solution in said evaporator wherebyheat is supplied to evapcrate solution in said evaporator and saidcompressed vapor is condensed. a -pump for withdrawing condensate fromsaid heat exchanger, a second pump for withdrawing solution from saidevaporator, electric motors for respectively op erating said pumps,means for de-energizing said respective motors upon overloading thereofand means responsive to the de-energizing of either of said motors fordiscontinuing the supply of solution to said evaporator and stoppingsaid compressor.

JOHN KIRGAN.

REFERENCES CITED The following references are of record in the iile ofthis patent:

UNITED STATES PATENTS Number Name Date Re. 21,129 Fox June 27, 193979,260 Savalle June 23, 18168 760,440' Forbes May 24, 1904 838,195LeSueur Dec. 11, 1906 1,213,596 DeBaufre Jan. 23, 1917 1,252,962Soderlund Jan. 8, 1918 1,361,834 DeBaufre Dec, 14, 1920 2,386,778Clafiey Oct. 16, 1945 FOREIGN PATENTS Number Country Date 117,806Australia Dec. 9, 1943 16,035 Great Britain 1897 OTHER REFERENCESTechnical Manual 5-2068, U. S. Army Corps of Engineers, Jan. 1945, pages8, 13, 14. Copy in Division 25.

